Cast iron is metallic and will eventually rust through. ABS plastic doesn’t have the same issue, but can be prone to cracking if it is under stress. Roots can find the slightest presence of moisture and once it finds the source it can grow into and break pipes and fittings. Until the pipe is repaired or replaced it will continue to require periodic cleaning which can be costly over an extended period of time or VERY expensive if you call the wrong plumber! Once-upon-a-time sewer replacement required a trench over the entire length of pipe being replaced.